1. Field of the Invention
The present invention relates generally to a solenoid valve and more particularly to a solenoid valve for opening and closing a fluid passage for gas such as air or vaporized gasoline to thereby control the flow rate and pressure of the flowing gas. This type of solenoid valve is installed on an automobile and useful as a duty control solenoid valve for controlling an amount of the canister purge that is, the amount of vaporized gasoline introduced from the gasoline tank or amount of air flowing in a bypass conduit of a throttle valve to an intake conduit through a canister.
2. Related Art
The conventional solenoid valve is constructed as shown in FIG. 1. The solenoid valve includes a bobbin 1 and an electric wire wound on the bobbin 1 to constitute an electro-magnetic coil 2. Both ends of the coil 2 are connected to a terminal 3. Outer periphery of the electro-magnetic coil 2 is protected by an outer cover 4 formed of mold resin. A connector housing for the terminal portion is formed unitary with the outer cover 4.
A stator core 5 acting as a stationary iron core is disposed in the center of the electro-magnetic coil 2. The stator core 5, a yoke 6 and a plate 7 surrounding the coil 2 constitute a magnetic path. A plunger 8 is slidably supported in a slide guide part 1a of the bobbin 1, one end of which faces the stator core 5. The other end of the plunger 8 is surrounded by a casing 100 which constitutes an inlet port 100a, outlet port 100b, fluid chamber 101 and a valve seat 100c so that a valve member 8a formed by an elastic material and fitted on the other end of the plunger faces the valve seat 100c. A spring 9 is disposed between the plunger 8 and the stator core 5 for urging the valve member 8a toward the valve seat 100c.
An O-ring 10 is fitted between the casing 100 and the plate 7 while an O-ring 11 is fitted between the bobbin 1 and the outer cover 4 to keep the air sealability between the components. Further, a rubber seat 12 is fixed between the yoke 6, stator core 5, bobbin 1 and the outer cover 4 to suppress an undesired vibration and obtain sealability.
The operation of the conventional solenoid valve thus constructed and shown in FIG. 1 will now be described.
When the terminal 3 inputs an electric signal from an outside device not shown, the coil 2 generates a magnetic field to thereby focus the magnetic field around the stator core 5, yoke 6 and plate 7 which constitute the magnetic path, and the plunger 8 acting as the movable iron core is magnetically attracted to the stator core side against the elastic force of the spring 9. The plunger 8 slides in through the slide guide part 1a of the bobbin 1 and, accordingly, the valve member 8a disposed on the end of the plunger 8 moves away from the valve seat 100c unitary formed with the casing 100, and the valve opens. In this condition, the gas starts to flow from the inlet port 100a to the outlet port 100b through the fluid chamber 101 and the valve seat 100c. The positions of the inlet port 100a and the outlet port 100b may be reversely changed to each other from the positions shown in FIG. 1. When the electric signal stops to actuating the coil 2, the plunger 8 is moved to slide by the elastic force of the spring 9 so that the valve member 8a comes into abutment against the valve seat 100c of the casing 100, and the valve closes the fluid path.
Since the conventional solenoid valve is constructed and operated as described above, the valve has a disadvantage that the open/close operation produces an undesirable air current noise in case that the open/close operation repeats in a very short period, for example, several tenth times per second. Of course, such a noise is generated when the open/close operation of the valve is occurred merely one time, however, it may not given rise to the noise problem since the one time operation causes only one sound. On the other hand, under the duty control, the valve opens and closes continuously in a very short period which produces the undesirable noise.
Unexamined Japanese Patent Application (OPI) No. Hei. 2-31227 discloses a silencer for suppressing the undesirable noise generated by the open/close operation of the solenoid valve. However, since recently an engine room of an automobile is required to be compact in size and, accordingly, an extra apparatus such as a silencer or the like should not be mounted on the solenoid valve since it causes the apparatus to undesirably become bigger and increases the component parts which increases a manufacturing cost.